function daysBetween(date1, date2) {
var DSTAdjust = 0;
// constants used for our calculations below
oneMinute = 1000 * 60;
var oneDay = oneMinute * 60 * 24;
// equalize times in case date objects have them
date1.setHours(0);
date1.setMinutes(0);
date1.setSeconds(0);
date2.setHours(0);
date2.setMinutes(0);
date2.setSeconds(0);
// take care of spans across Daylight Saving Time changes
if (date2 > date1) {
DSTAdjust =
(date2.getTimezoneOffset() - date1.getTimezoneOffset()) * oneMinute;
} else {
DSTAdjust =
(date1.getTimezoneOffset() - date2.getTimezoneOffset()) * oneMinute;
}
var diff = Math.abs(date2.getTime() - date1.getTime()) - DSTAdjust;
return Math.ceil(diff/oneDay);
}
var projectLength = 0;
// validate form entries with checkDate() function from Recipe 2.12
var startField = document.entryForm.startDate;
var endField = document.entryForm.endDate;
if (checkDate(startField) && checkDate(endField)) {
var startDate = new Date(startField.value);
var endDate = new Date(endField.value);
projectLength = daysBetween(startDate, endDate);
}
if (projectLength > 0) {
alert("You\'ve specified " + projectLength + " days for this project.");
}